The present invention relates to a cordierite ceramic and a method for manufacturing the cordierite ceramic.
Cordierite ceramic shows high heat resistance, low thermal expansion and high thermal shock resistance and therefore is in wide use as, for example, a catalyst carrier or a filter for purification of exhaust gases emitted from internal combustion engines of automobiles and the like. In industrial production of this cordierite ceramic, there are often used natural raw materials such as kaolin, talc, aluminum-containing oxides, hydrates and the like. However, these raw materials contain impurities such as titanium oxide, iron oxide, alkali or alkaline earth metal oxide and the like. Being natural raw materials, they differ in the amounts of components contained, depending upon, for example, the place of origin, the place of mining, the timing of mining.
It is known that ceramics, when containing impurities, cause color change in the resulting products (for example, see JP-A-6-172016).
Cordierite ceramic as well shows, in some cases, color change depending upon the compositional fluctuation of raw materials, mainly the above-mentioned impurity components. In particular, depending upon the amounts and proportions of titanium oxide, iron oxide, and the like contained in raw materials, cordierite ceramic changes its color from light yellow to reddish brown. Further, there is a case of coloring in spots, which gives heterogeneous appearance.